I searched the wiki and didn't find any mention of Dak Prescott making that exact quote — it's not covered in the curated news pages. That said, I can tell you the Cowboys offense was legitimately elite last season: 2nd in total yards, 5th in scoring (27 PPG), with Prescott throwing for 4,552 yards (#3 in the NFL). (from the Dak Prescott page and Dallas Cowboys page)
The wiki notes that NFL.com called it a "Super Bowl-caliber offense" and the team returned all 11 offensive starters. So while I can't confirm the exact quote, the confidence would've had some stats to back it up. If you saw that somewhere in the news recently, I just don't have it in my current database.